Applicability of Mg -Zn-(Y, Gd) alloys for engine pistons

Commercial magnesium alloys have a great potential for structural applications in automotive due to their significant weight saving. However, they have poor creep resistance at temperature over 125 degrees C, thus making them inadequate for power train applications such as engine pistons, which are operated at temperature up to 300 degrees C. Recently, creep resistant magnesium alloys with rare-earth elements and Zn have been developed, hence the applicability of Mg-Zn-(Y, Gd) alloys for engine pistons was investigated in this paper. Gravity casting was performed with Mg-Zn-(Y, Gd)-Zr alloy, followed by T6 treatment. Effects of the amount of alloying elements on the mechanical properties of tensile strength and creep strain were evaluated. Nominal composition of Mg-2Zn-11Y-5Gd-0.5Zr was selected for the actual piston cast trial and its high cycle fatigue test was conducted comparing to the current aluminum cast alloy of A336 (JIS AC8A) for pistons. At room temperature, the fatigue strength is 27% lower than A336, while it is 35% higher at 300 degrees C. It is suggested that Mg-2Zn-11Y-5Gd-0.5Zr alloy shows attractive high temperature mechanical properties higher than A336, hence it is promising as a candidate material for the engine piston application.